Fiber, Part II: Soluble vs. Insoluble

Last month, we looked at what fiber is, and touched on what it does. I explained (or at least I tried to) the differences and similarities between soluble and insoluble fiber. This month, I want to explain why the differences between soluble and insoluble actually matter, and then get into specifics on:

• detoxification and liver health
• weight management
• cholesterol and heart disease
• regularity and colon health
• diabetes and metabolic syndrome

Finally, next month, I want to go over specific types of fiber, and fiber-rich foods.

Soluble vs. Insoluble Fiber: Toxins, Regularity, and Blood Sugar

Soluble fiber is like a sponge. It attracts liquids, expands, and thickens. It’s good at absorbing things, and generally taking up space.

•   Insoluble fiber is like a scrub brush. It doesn’t absorb much, and doesn’t expand. It’s especially good at moving things along, a.k.a. “keeping you regular.”
•  (And I’ll repeat what I said last month: the properties of soluble vs. insoluble fiber are not mutually exclusive, and most foods will have at least a little bit of both anyways…)
•  It’s soluble fiber’s ability to absorb things that makes it so special. First of all, soluble fiber can absorb toxins. It can absorb hormone residues. It can absorb cholesterol. And yes, it can also absorb good things, like nutrients, and pharmaceutical and herbal medicines. (Fiber isn’t smart – it can’t “tell the difference.”)

Don’t worry too much about this: fiber doesn’t leave the gut, so it can’t bind to good things in tissues or blood. If you simply take your vitamins or drugs at a different time, you should be fine.

By the same token, fiber doesn’t pull bad things (“toxins”) out of the blood, either. However, your liver does. And when your liver filters toxins out of the blood, it dumps them out with the bile into the small intestine… where the fiber can bind and sequester them. This is important because, while the small intestine leads to the large intestine, which in turn leads to the outside world, it’s also a place we can absorb a lot of things from. So without adequate fiber, the liver dumps its toxins out into the small intestine… and then they get reabsorbed right back into the bloodstream.  So they need to make a second, sometimes a third or fourth pass through the liver. This is first of all highly inefficient. It also puts an additional strain on the liver, and burdens the body with more toxins.

So even though fiber doesn’t have any direct impact on the liver, it still stands as one of the most important nutrients for liver health. And since toxins can hurt every organ system of the body, it’s safe to say that fiber stands as one of the most important nutrients for the health of the body in general. Even though it never gets into the body.*

Soluble fiber also does something similar with sugars. It doesn’t bind or neutralize them in any lasting way. But like a sponge holding water, fiber holds them for a little while, releasing them slowly for absorption. So let’s say you eat a high-glycemic meal, something loaded with sugar or fruit juice or simple starches. If you also eat some fiber, the sugar doesn’t shock your bloodstream all at once.  (There’s a reason why apple juice might make a kid hyper, but whole apples won’t).

Blunting these spikes in blood sugar is of massive importance to both short-term and long-term health. Here’s what happens when your blood sugar spikes.

• Short-term: hyperactivity, like some kids get
• Longer-term: cell damage, like diabetics get. Over years and decades, this raises the risk of heart disease and cancer, among other things
• The more time you spend with high blood sugar, the worse your body gets at handling it. Over time, this will leads to Type II diabetes, a.k.a. metabolic syndrome. Want to read more about metabolic syndrome? The Blood Sugar Solution is a wonderful, accessible book on the subject by Mark Hyman, from the Ultra Wellness Center in Lenox, MA. Don’t take my word for it, though. The front-cover endorsement is from Bill Clinton, who’s looking pretty svelte these days.

And when the blood sugar gets too high, the body tends to overcompensate by lowering it too far. When your blood sugar is too low, you can expect the following.

• Short term: irritable, cranky, fatigued foggy-brained malaise, a.k.a. “the sugar blues.” Our energy is depleted, our serotonin levels drop… And of course we end up craving more starchy and sugary foods for a quick fix to feel better… which in turn sets up the cycle to make us feel even worse further down the road.
• Weight gain. Because the body doesn’t magically “lower” blood sugar into thin air. The calories have to go somewhere. You know where they go.
• Stress. Low blood sugar creates a state of physiologic stress which is really no different than sleep deprivation, exposure to cold, overexertion, etc. The adrenals respond to low blood sugar by kicking out cortisol and adrenalin, which help mobilize sugar stores in the liver. But these are also stress hormones. When you read about the effects of stress on the heart, on the mind, on long-term immunity, etc., please bear in mind, low blood sugar does all of this.

And fiber – especially soluble fiber – makes it all better.

I should also mention that foods naturally high in fiber tend to be generally healthy. In nature, fiber just seems to correlate with nutrient content. Seriously, I challenge you to come up with a naturally high-fiber food that isn’t good for you!

More about soluble fiber vs. insoluble. Insoluble fiber can sometimes be a little “harsh” for people with sensitive guts. Again, think of the sponge vs. the brush. This certainly doesn’t mean that insoluble fiber is bad! Just that, if it bothers you, switching to more soluble fiber might help.

Also, I talked about soluble fiber being good at absorbing things, and insoluble fiber not so much… There’s a major exception to this rule. Certain kinds of insoluble bran – wheat bran in particular – are rich in compounds called phytates, which are generally healthy, but tend to bind microminerals such as iron, zinc, and manganese. This doesn’t mean you can’t take your iron pill with a small slice of whole grain toast. But those super-wheat-bran breakfast cereals and muffins might be a bit problematic.

Weight Control: Fiber helps control weight three ways. First, through all that stuff I mentioned about blood sugar control. Second, by simply filling you up. Fiber (especially soluble fiber) absorbs water, and takes up space. And finally, because you tend to have to chew more on high-fiber foods, they satisfy psychologically.

Stepping beyond theory, there is so much really good research here. A lot of epidemiologic research where people who eat more fiber tend to weigh less. But also some pretty solid clinical trials.      Obviously, obviously, different kinds of fiber work differently, in different people, with different diets, in different doses and dose regimens. Unfortunately, there’s no conclusive ranking or definitive numbers I can give you. But if you read over some of the research, you can’t help but walk away impressed. Almost any time overweight people are put on diets with higher fiber content, you see weight loss. You usually see cholesterol and blood pressure get better, too. People with higher-fiber diets not only lose more weight eating the same number of calories, they also find it easier to eat fewer calories, probably because fewer calories are needed to feel full, and satisfied.

The research on fiber pills and powders is a little more mixed, but generally still positive. By far the most impressive research has been with a kind of fiber called glucomannan, or konjac fiber. Glucomannan absorbs a ridiculous amount of water, expanding to something like 200 times its dry volume. In a number of small trials, glucomannan supplements (1 gram before meals, with a big glass of water) tended to produce an average weight loss vs. placebo of 3.5 pounds per month.

Maybe 3.5 pounds doesn’t sound like a lot. But consider that this was achieved a) without any additional effort; and b) in a way that promoted general health anyways. That’s pretty impressive. You know, we’re always getting excited about the “newest” weight loss supplement touted just last week on television.  Well folks, here’s your glucomannan. And 3.5 pounds x 12 months = 42 pounds a year. Will the math be that simple for you? To be honest, probably not. But even if we cut those numbers in half, just imagine next Fourth of July, being 21 pounds lighter.

One more argument for supplements. It’s well known that high protein, low starch diets tend to promote weight loss. But high protein diets also tend to be very low in soluble fiber. Fiber supplements can work around that.

Please be aware that the ability of glucomanan to absorb water and swell can be problematic if you have a hard time swallowing pills – they might get stuck in the throat. And don’t take much more than the standard dose. More is not always better…

Regularity and Colon Health: I’m not going to cite research on regularity. You already know what happens in the morning when you get enough fiber. And it makes your whole day better!

I should mention, however, that some people have a hard time with fiber because it can make them a bit gassy and bloated. This is often because it takes a while for the gut flora (our friendly, and sometimes unfriendly, bacteria and yeasts) to acclimate to a higher-fiber diet. Ease up. Allow time for gut flora to get used to the additional fiber.

I should also mention that some people, occasionally, find fiber makes them more constipated. Fiber, especially soluble fiber, needs water to work, because it absorbs water to bulk up and take up space. When there isn’t enough water, it can get dry and compacted. So, drink enough water, okay?

Cholesterol and Heart Disease: Like with weight loss, boatloads of research here, and it’s hard to summarize. So allow me to defer to a meta-analysis published in the American Journal of Clinical Nutrition in 1999. Pooling data from 67 controlled trials on fiber and cholesterol, the research team concluded that “The effect is small within the practical range of intake… Increasing soluble fiber can make only a small contribution to dietary therapy to lower cholesterol.”

I think this is a fair assessment. Fiber alone usually won’t lower cholesterol as dramatically as a statin drug, or an herbal medicine like Artichoke, Red Yeast Rice, or Guggulipid. It certainly doesn’t lower cholesterol as quickly. And that’s where the big caveat comes in with this research. The average length of the 67 trials here was 49 days – about a month-and-a-half. There have been a few trials that have gone longer, that seem to imply a more pronounced benefit.

And fiber tends to improve other parameters of heart health, not just cholesterol. For example, body weight, blood pressure, blood sugar, and liver health all tend to get better with fiber. These all can be just as important as cholesterol in predicting heart attack and stroke. And these, too, often take a little longer to establish themselves.

What I tell people in the store is if you flat-out want to see cholesterol number drop as quickly as possible, look at Red Yeast Rice. Maybe Artichoke. Or Guggulipid, if your ratio is also off. But if you want to see general health improve, along with a significant reduction in wide variety of heart disease risk factors, look first to fiber (and the fish oil, and the darkly colored berries).

The END next month.

… Adam Stark